Seismic surveying is a vital part of exploring for oil and gas. That makes it critical to producing the energy we need to power our homes and businesses.
Oil and gas explorers use seismic surveys to produce detailed images of the various rock types and their location beneath the Earth's surface and they use this information to determine the location and size of oil and gas reservoirs.
Sound waves are bounced off underground rock formations and the waves that reflect back to the surface are captured by recording sensors. Analysing the time the waves take to return provides valuable information about rock types and possible gases or fluids in rock formations. This is similar to the use of ultrasound in medicine.
In marine operations, a specialised vessel tows a “seismic streamer”, or a collection of cables with seismic sources and hydrophones attached. The seismic sources use compressed air to produce acoustic energy. The hydrophones capture the returning sound waves.
Hydrophones and geophones are highly sensitive. They are deployed in clusters to optimise the reception and recording of sound waves. This provides information about rock types and possible oil or gas deposits.
Onshore seismic operations usually use specialised trucks that carry a heavy plate that is vibrated to generate a seismic signal. Onshore seismic has been used in sensitive locations — including central Paris — without damaging buildings or the environment.
Seismic processing requires powerful computers,sophisticated software and specialised skills
Once the seismic has been processed, it must be interpreted by geophysicists. The results will be compared with other data (such as rock samples, regional well/drilling results and known geology) to enhance the accuracy of the interpretation. This often produces detailed understanding of geology to depths of more than 10km.
Seismic information is used to accurately plan locations for wells, reducing the need for further exploration and minimising environmental impact.
Contrary to the claims of some environmental groups, seismic surveying is a very well-understood science and a very safe industry practice.
More than four decades of seismic surveying and numerous research projects have shown no evidence that offshore seismic surveys harm marine animal populations or ecosystems.
The responsible precautions taken by industry mean the effects of man-made noises, such as seismic surveys, on marine mammals are insignificant. For example, whale populations can be found all along Australia's coastlines and seismic operators employ extensive precautions to minimise any disturbances to these animals. Whale populations in Australia continue to thrive — humpback whale populations are increasing at close to their biological maximum, more than 10 per cent a year.
There is much more offshore oil and gas activity on Australia’s west coast than on its east coast, but the rates of humpback population increase are almost identical. There is no evidence that seismic surveys off Western Australia have harmed Australia’s humpback whale populations.
The sound from seismic surveying is comparable to many naturally occurring marine sounds — including those made by animals themselves.
|Source||Sound Intensity & Pressure (dB re 1µPa @ 1m)||Frequency (Hz)|
|Seafloor volcanic eruption||>255||Varied|
|Lightning strike on sea surface||250||Varied|
|Seismic acoustic source||Up to 255||<200|
|Sperm whale click||Up to 235||100 - 30,000|
|Bottlenose dolphin click||Up to 229||Up to 120,000|
|Ship sound (close to hull)||200||10 - 100|
|Blue whale vocalisation||190||12 - 400|
|Ambient sea sound||80 - 120||Varied|
Adapted from: Swan, JM et al, 1994 environmental implications of offshore oil and gas development in Australia, APPEA, Australia
The oil and gas industry uses extensive environmental management plans to ensure all offshore operations are conducted safely and responsibly.
Seismic surveys cannot begin when certain species are too close to the sound source. Once the survey does begin, the seismic sources are turned up slowly during a 'ramp-up' period of about 30 minutes, so that marine animals are not startled and can move away.
The slow approach of ships (generally only a few knots) provides further time for marine animals to move. Survey timing, observation zones, low-power zones, acoustic monitoring and many other measures further reduce any interactions with – or effects upon – marine species.
For more than four decades, seismic surveying and countless research projects (both in Australia and world-wide) have shown no evidence to suggest that sound from oil and gas exploration activities in normal operating circumstances has harmed marine species or marine ecological communities.
Nor have studies found any significant disruption of marine animal behaviours that would affect survival or reproduction.
One of the most comprehensive research studies carried out anywhere in the world was conducted by Woodside in 2007 in and around Scott Reef off the north-west of Australia.
This study was done by leading researchers from all over the world. They examined the impacts of a seismic survey on marine life and concluded that it caused:
Many other studies have been conducted by various organisations around the world.
In Canada in 2004, teams of scientists prepared major literature reviews of the primary and secondary literature that reported on experimental studies and field monitoring of the effects of sound, particularly seismic sound, on marine organisms. These have been published as Review of Scientific Information on Impacts of Seismic Sound on Fish, Invertebrates, Marine Turtles and Marine Mammals.
These studies have not found evidence that suggests any link between seismic surveys and adverse impacts on marine life.
The effects of seismic on plankton
A study published in an online journal, Nature: Ecology and Evolution, on 22 June 2017 has challenged the scientific understanding on how sound from seismic surveys can affect plankton.
To date, scientific studies have indicated that the sound related to seismic surveys affect plankton communities at a distance of metres to tens of metres.
But research by Associate Professor Robert McCauley from Curtin University's Centre for Marine Science and Technology challenges this belief. According to this research, marine seismic surveys can affect plankton at significantly larger distances from the commercial seismic array than previously believed.
The oil and gas industry has significant concerns with this research, including overall replication, sample size, conclusions inconsistent with the data and the lack of a biologically plausible mechanism for the observed plankton mortality and changes in abundance. However, consistent with its commitment to the highest standards of environmental protection, the industry has moved to further research the effects of seismic sound on plankton.
APPEA commissioned the CSIRO to model the potential local and regional impacts of a typical marine seismic survey in the North West based on the McCauley et al results.
The modelled seismic survey ran for 36 days (late December 2016 to early February 2017) and covered an 80km x 36km area. It took a precautionary approach by assuming that McCauley's main findings were accurate, and used McCauley's plankton mortality estimates and spatial ranges.
Early results from this CSIRO research indicate that although zooplankton biomass within the survey area was reduced, it recovered only three days after the completion of the survey. Importantly, there appeared to be no discernible regional impacts from the modelled seismic survey.
Read the report
More research is being planned to assess potential impacts of seismic survey sound on plankton communities.
Oil and gas operators and marine research organisations are discussing the exact timing of this research. This research is part of a three-year study through the Australian Institute of Marine Science that will seek to enhance understanding of how seismic sound affects the marine environment.
Australian seismic surveys are subject to extensive environmental assessment approval procedures under the Offshore Petroleum and Greenhouse Gas Storage Act and regulations administrated by the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA).